Field of the Invention
The present invention relates to a lens barrel to be used for optical apparatuses such as digital cameras, video cameras and interchangeable lenses.
Description of the Related Art
The above-described lens barrel includes ones having a mechanism which moves, by utilizing rotation of a rotatable barrel rotatable about an optical axis in a circumferential direction, a holder that holds an optical element such as a lens (the holder is hereinafter referred to as “a lens-holding frame”) in an optical axis direction for focusing and zooming. Such a mechanism typically uses a cam barrel as the rotatable barrel having a cam portion, a guide barrel as a base barrel having a straight guide portion extending in the optical axis direction and a cam follower engaged with both the cam portion and the straight guide portion. The cam follower is fixed to a lens-holding frame by a fastening member such as a screw. Rotation of the cam barrel in a circumferential direction causes the cam follower to be driven by the cam portion in the optical axis direction while being guided by the straight guide portion in the optical axis direction, which moves the lens-holding frame in the optical axis direction.
In order to highly accurately move the lens-holding frame together with movement of the cam portion, it is important to stably fix the cam follower at a predetermined position on the lens-holding frame without a positional shift. It is thus desirable to attach the cam follower to the lens-holding frame with good accuracy and to engage the cam follower, the cam portion and the straight guide portion with one another without backlash.
In addition, it is necessary to prevent, even when environment such as temperature changes after assembling of the lens barrel, a decrease in optical performance caused by, for example, tilt of the lens-holding frame due to an increase in engagement backlash between the cam follower, the cam portion and the straight guide portion.
Japanese Patent Laid-Open No. 2000-002830 discloses a lens barrel in which one of a base barrel and a movable barrel is provided with, at its two mutually circumferentially adjacent phases, straight grooves each extending in an optical axis direction and respectively engaging with engagement members fixed to the other of the base barrel and a movable barrel, which prevents the movable barrel from tilting.
However, in the lens barrel disclosed in Japanese Patent Laid-Open No. 2000-002830, the movable barrel is moved in the optical axis direction by the engagement of the engagement members fixed to the base barrel with the straight grooves formed in the movable barrel and engagement of a drive pin provided to a rotatable focus ring with a lead groove formed in the movable barrel. The movable barrel is linearly moved in the optical axis direction without rotation in the circumferential direction. This configuration can prevent the movable barrel from tilting by the engagement members engaging with the straight grooves, but cannot prevent a positional accuracy of the movable barrel in the optical axis direction from being affected by dimensional tolerances of the engagement members and the drive pin because the engagement members engaging with the straight grooves and the drive pin are separately provided. Furthermore, presence of the dimensional tolerance or an assembling error of the engagement members engaging with the straight grooves generates twisting (prying, wrenching, galling) in movement of the movable barrel. The twisting increases a load, leading to a deterioration in operational feel of the focus ring.